I'm so sorry Angelique, it must be incredibly difficult to watch your son not only suffer with his condition, but his relationship breakdown as well. He's having a tough time, and his pride may be affected as well if he's having to rely more on you.
Have you spoken to your GP? They may be able to recommend some treatment options for your sons PTSD, such as counselling or medication. His reliance on alcohol will continue to lower his mood, perhaps you could help him develop healthier coping mechanisms. I don't know the extent of his condition but is he able to use computer games, board games, puzzles? These activities stimulate the mind and encourage creativity and resourcefulness, helpful if he's lacking in motivation. Plus, they are suitable for the comfort of a bedroom.
I'm sorry I can't be of more help, you definitely would benefit from specialist advice. This must all be very hard on you too so please take care of yourself, I'm sure your son would benefit from seeing you have confidence and happiness so I hope you can stay strong for the benefit of each of you. I wish you well.